Well, I never experienced R6034 error myself. I suggest to
open your executable with Depends utility (and run
profiling, if necessary). It can reveal DLL loading problems
and pinpoint offending DLL exactly. In theory, if EXE and
DLL both link to dynamic version of CRT, then the same CRT
library should be used by both components.
Also, if you can re-create you project from scratch by
adding new components one by one, it worth trying. Then
you'll get clear indication when projects stops working.
Sorry I couldn't give more specific advise.